1. Field of the Invention
The present invention relates generally to digital computer systems, and more specifically to a system and method for testing memory in a computer system.
2. Description of the Prior Art
When operation of a computer system is started, it is common practice to test the main system memory by writing a preselected data pattern to every memory location and reading the memory locations back to see if they are correct. This allows the system to determine which memory locations are good and mark the bad locations so that they will not be used. A memory test is generally performed when power is first applied to the system, and sometimes after certain system resets. The process of restarting the computer system, of which such memory test is a part, is often referred to as the system boot (bootstrap), or IPL (initial program load).
As the amount of main memory used in computer systems increases, a longer period of time is required to test the system memory. Computer systems with several tens of megabytes of memory have become common only relatively recently. Future systems are expected to have one or more hundreds of megabytes. The time required for testing the main memory in such systems is becoming quite long. Since programs cannot be run using the system memory until it has been tested, a significant delay is encountered before the system can be used for productive applications.
With some computer systems, the system memory test at boot time is simply skipped, or performed only at the option of a user. In many cases, skipping the memory test causes no problem because of the high reliability of computer semiconductor memories. However, problems do occasionally occur and the risk of not performing the check can be high. As the amount of main memory used in computer systems increases, the chances of one or more bad memory locations occurring increases. This means that memory testing, in general, is more important for those computer systems for which it takes the longest amount of time.
It would therefor be desirable to provide a system and method for testing all of the main memory of a computer system. It would be further desirable for such a system and method to test system memory without requiring long delays when a computer system is booted.